The invention relates to a method for recovering aroma concentrate from a caffeine- or theobromine-comprising food base material, such as coffee or tea, and in particular cocoa, at least comprising the steps of:
introducing the food base material into an aqueous extractant and incubating the food base material at a suitable temperature and for a suitable period, substantial extraction of the aromas taking place to form an aqueous food extract,
pervaporating the food extract using a hydrophobic pervaporation membrane to form a food aroma permeate,
recovering the permeate to obtain the aroma concentrate.
The term xe2x80x9caroma concentratexe2x80x9d in this context refers to an isolated mixture of aromatic substances as it exists in the base material, said mixture being present in a solvent, particularly water. Preferably, the recovered aroma concentrate substantially has an aroma profile which matches that of the base material, which is to say that the concentration ratio of the aromatic substances in the recovered aroma concentrate according to the invention substantially matches that of the aromatic substances in the base material. An aroma profile can be determined by methods known in the art, for example by means of dynamic headspace analysis (Dynamic Headspace; see T. P. Wampler, in Techniques for analysing food aroma, edited by P. Marsili, 1977, pp. 31-33, ISBN 0-8247-9788-4, and references therein). The invention therefore does not relate to the purification of a single chemical compound.
In the art, aroma concentrates obtained with the aid of steam distillation and liquid extraction are known. Reference is made in this context to U.S. Pat. No. 3,579,349 and to Food Tech Europe, December 1994/January 1995, pp. 48-54, respectively.
In the case of steam distillation, the high temperature results in thermal degradation of a considerable fraction of the aroma molecules, the product not having as full a taste as a result. In the case of liquid extraction, use is often made of organic solvents which must be removed completely from the extract obtained, which entails high costs and is problematic from an environmental point of view. Reference can be made in this context to DE-C-2 055 030.
U.S. Pat. No. 3,492,027 discloses a method for preparing a cocoa aroma by extracting cacao shells in boiling water. Such an extract, however, contains suspended particles, is brown in colour and contains purines, catechols and other water-soluble components such as proteins, carbohydrates and minerals, which considerably hamper further concentration of the desired aroma. In this context, purines mainly mean caffeine and theobromine. Catechols such as catechol, epicatechol and epigallocatechol are also known as antioxidants.
The pervaporation process is known per se in the art, see for an overview, e.g. Baudot and Marin, Food and Bioproducts Processing (1997) 75, pp 117-142. For separating azeotropic mixtures and for the dealcoholization of beverages, see for example DE-A-3 804236 and Karlsson and Tragardh, Trends in Food Science and Technology, 1996 (7), pp 78-83.
Also known per se in the art is the use of pervaporation to isolate individual aroma concentrates, i.e. to purify and separate individual chemical compounds (See e.g. DE-A 4 421 682).
Pervaporation is used especially to isolate aroma components from fruit juices, for example to obtain an aroma concentrate from apples. To this end, the juice is obtained from apples, and this juice is then subjected to pervaporation (see for example Borjesson et al., Journal of Membrane Science, Volume 119, 1996, pp. 229-239). The permeation conditions can be optimized by those skilled in the art in a simple manner, although in the case of fruit juices it did not prove possible to obtain an aroma concentrate having a satisfactory original aroma profile.
JP-A-05049840 describes a method for isolating a biologically active aroma concentrate from leaves of the medicinal plant Eucommia ulmoides. To this end, an aqueous extract of the leaves is subjected to permeation or pervaporation, the concentrate being recovered, however, on the primary side of the membrane, i.e. as the retentate. Pervaporation is thus used solely as a dehydration method; the aroma constituents do not pass through the pervaporation membrane.
A method of the above mentioned type for isolating seperate aroma components from in particular food juices is described in SE-C-500 579. In order to obtain desired concentration of aroma components, the hydrodynamics of the seed are altered. However, an aroma concentrate having an original aroma profile is not obtained.
The process of employing pervaporation to isolate an aroma concentrate having an aroma profile which substantially matches that of the base material in question (herein also referred to as xe2x80x9coriginal aroma profilexe2x80x9d) is not known, however.
Surprisingly it is found that in the case of caffeine- and theobromine-comprising food base materials, particularly in the case of cocoa-containing base materials, pervaporation at elevated temperatures (i.e. 30xc2x0 C. or more) can be used without the original aroma profile being lost. It is precisely at lower pervaporation temperatures that important aromatic substances will be partially retained in the retentate, so that a full aroma having the original aroma profile cannot be obtained.
In this context it is noted that pervaporation in the art, i.e. the isolation of odorous substances and flavourings, i.e. aromatic compounds, in contrast is carried out at lower temperatures. Those skilled in the art will choose precisely the pervaporation technique as a separation technique for mixtures comprising temperature-sensitive components (such as fruit juices, for example) and will therefore employ low temperatures. If such components are not present in the mixture to be separated they will predominantly use other thermal techniques such as steam-stripping and vacuum distillation.
The present invention therefor provides an improved method for recovering aroma concentrate from a caffeine- or theobromine-comprising food base material, such as coffee or tea, and in particular cocoa, of the above-discusses type, and is characterised in that the temperature of the extract and the permeate, respectively, during the pervaporation is more than 30xc2x0 C.
It was found that the use of pervaporation according to the invention affords excellent aroma concentrates, in particular cocoa aroma concentrates, without valuable aromatic substances being lost during the preparation, which is to say that it is possible, via the method according to the invention, to obtain an aroma concentrate having an aroma profile which substantially matches that of the base material from which the aroma concentrate has been obtained (see example). It is also possible, via the method according to the invention, to obtain an aroma concentrate which substantially comprises all the desired aromatic substances from the base material which can be perceived by human taste and smell, as a result of which a xe2x80x9cfullxe2x80x9d and xe2x80x9ccompletexe2x80x9d aroma concentrate is obtained.
In addition, temperatures above room temperature are advantageous, as the fats present in the feed are then dissolved and as such cause fewer problems with clogging and fouling of the membrane. It should be noted that the said fats substantially do not pervaporate through the permeation membrane; consequently, the permeate is substantially fat-free.
It is important to note that the present inventors have established that as a result of pervaporation substantially no purines and catechols are present in the permeate obtained, the aroma becoming less bitter and astringent as a result, which is highly advantageous for preparing, for example, a purine-free coffee aroma, tea aroma or cocoa aroma. An aroma is thus obtained which in terms of smell and taste largely matches the smell and taste, respectively, of the starting material. Thus a cocoa aroma obtained according to the method of the present invention has a taste which is qualitatively comparable with the food base material cocoa powder.
Caffeine- or theobromine-comprising food base materials to be mentioned as suitable for use in the method according to the present invention include coffee beans, in particular of the varieties Coffea arabica, Coffea canaphora robusta and Coffea liberica, tea leaves, in particular of Damillisa sinensis and Camelia assamica, and cocoa-comprising foods, where cocoa-comprising foods include cocoa powder, cacao cake, cacao mass, cacao nibs and cacao shells, in particular of the variety Theobroma cacao L. Preferable among cocoa-comprising foods are cocoa powder and cacao cake. The food base materials suitable for the method according to the present invention are by no means limited to the abovementioned base materials. If desired, other plant parts which comprise caffeine or theobromine can be used to obtain a substantially caffeine- and theobromine-free extract. Substantially caffeine- and theobromine-free is meant to indicate that the concentration of these substances in the aroma is less than 0.0001 wt % (xcx9c0.001 g/l).
The food base material is introduced into an aqueous extractant, followed by incubation at a suitable temperature and over a suitable period, substantial extraction of the aromas taking place to form a food extract.
The term xe2x80x9csubstantial extractionxe2x80x9d is understood to mean that as a result of extraction at least 10% of the aromatic substances present in the ultimate aroma concentrate, based on the total amount of the substance in question in the base material to be extracted, is taken up into the extractant; preferably this is at least 30%, yet more preferably at least 50% and most preferably more than 70%.
The advantage of aqueous extraction is that the solid particles and especially the not readily separable colloidal suspended particles need not be separated. It is sufficient for the coarser particles to be separated, for example by screening, to prevent blockages in the pervaporation.
It was found that the use of such an extraction step prior to the pervaporation allows a very good, full and substantially fat-free aroma to be obtained. As it is important that the membrane configuration will not become blocked during the pervaporation, it is advantageous to subject the extract to coarse filtration prior to the pervaporation step. It will be evident to those skilled in the art that the maximum particle size in the extract will depend on the membrane configuration to be used. If, for example, coated hollow fibres are used as the membrane configuration (see below), the maximum diameter of the particles in the extract should be smaller by approximately a factor of from 5 to 15, preferably a factor of 10, than the internal diameter of the hollow fibres. It should also be noted that a cocoa extract contains both dissolved and suspended particles.
Extracting the food base material, followed by pervaporation, renders any supplementary purification or acidification step of the extract unnecessary and enables the method to be implemented in mild process conditions, which allows valuable aromatic substances to be retained.
The term xe2x80x9caqueous extractantxe2x80x9d refers to a liquid which mainly comprises water and into which preferably no fat or as little fat as possible is taken up.
For particular applications it may be advantageous for the extractant used to be a water-alcohol mixture, the alcohol content preferably being between 10-40% (v/v). By means of such an extractant it is possible to extract even aromas which are less soluble in water, a xe2x80x9cfullerxe2x80x9d aroma being obtainable as a result if desired. The term xe2x80x9cfullerxe2x80x9d means that aromas are obtained in a higher concentration and in a more natural ratio, as also present in the base material. However, if an organic solvent, for example, is used as an extractant, this should be removed substantially completely from the product obtained, since the product otherwise cannot be used for foods; moreover, the organoleptic properties are often impaired.
To avoid a supplementary purification step, the extractant is preferably water. This means, inter alia, tap water, distilled water and pyrogen-free water. It was found that if the extractant is water, a high-quality extract is obtained, using which a very xe2x80x9cfullxe2x80x9d aroma product is obtained after pervaporation.
If water is used as the extractant, the weight ratio of food base material: water is preferably between 1:5 and 1:25. If the ratio is lower, the yield will be small, and if the ratio is higher, the base material, in particular cocoa, is often difficult to dissolve or suspend, respectively, in the water. Preferably, the base material: water ratio is between 1:9 and 1:11. It was found that with such a ratio at room temperature it is possible to dissolve enough base material for a good yield of aromas to be achievable. The advantage is that dissolution or mixing can be carried out at room temperature, so that warming is unnecessary. It is also possible to opt for the base material during the extraction to be dissolved or suspended, respectively, in the water. If the extraction takes place at a higher temperature, the base material will dissolve or become suspended, respectively, more efficiently in the extractant, causing a more concentrated material to be subjected to extraction, thus permitting an increased yield.
Most preferably, the ratio base material: water is 1:10. It was found that at such a ratio a good-quality extract can be obtained, the base material being dissolvable or mixable, respectively, in the water at room temperature prior to the extraction, without troublesome agglomeration or sedimentation of the base material taking place.
Advantageously, the temperature during the extraction is 90-125xc2x0 C., since at lower temperatures not all the aromas are extracted, resulting in a lower-quality extract being obtained. At elevated temperatures there is a major risk of thermal degradation, valuable cocoa aromas being lost as a result. As already stated hereinabove, the cocoa can also be dissolved in the extractant during the extraction, more cocoa being capable of being dissolved owing to the higher temperature used as a rule, without troublesome agglomeration or sedimentation of the cocoa taking place in the extractant. In this context, reference is made to Example 1.
The efficiency of the extraction is determined not only by the extraction temperature used, but also by the duration of the extraction. It was found that with an extraction at 100-125xc2x0 C., preferably between 105 and 115xc2x0 C., most preferably between 105 and 110xc2x0 C., an extraction time of one hour affords a good extract which can be subjected to the following pervaporation step. Reference is made to Example 2. It is obvious to those skilled in the art that at higher extraction temperatures it is possible to extract for a shorter time and the extraction period should be limited so as to cause no degradation of desired aromatic substances. On the other hand it is obvious that if lower extraction temperatures are used the extraction period will be longer.
The food in liquid and/or pumpable form is preferably cooled, prior to the pervaporation process, to below 80xc2x0 C., as the polymeric pervaporation membranes used often become damaged above 80xc2x0 C., thus adversely affecting the separation efficiencies of the pervaporation process.
The thickness of the pervaporation membrane is preferably at most 10 xcexcm, more preferably at most 5 xcexcm, most preferably at most 3 xcexcm. In the art, on the other hand, pervaporation membranes having a thickness of 10 xcexcm or more are used, to obtain a high selectivity for purifying individual aromatic substances. It was found that it is precisely with a thinner membrane according to the invention that an aroma concentrate having the original aroma profile can be obtained, with adequate selectivity against undesirable substances such as caffeine, theobromine, fats, catechols, proteins; furthermore, the amount of water which passes through the pervaporation membrane is limited. Likewise, it is possible using membranes having a thickness according to the invention, to achieve an improved yield.
It was found that if during the pervaporation process membranes are used which comprise coated hollow fibres, a product is obtained which has a full cocoa aroma. By making use of such hollow-fibre membranes it is possible to fabricate modules which have a low volume/surface ratio, thereby permitting a compact configuration of the membrane system with a high through-flow capacity. Equally, however, it is possible to use other membrane configurations such as flat films or spiral systems, although hollow-fibre membranes are to be preferred. Whilst homogeneous flat membranes do have good separation characteristics, they meet the mechanical requirements to a lesser extent and result in too low a yield. Spiral configurations often lead to problems with clogging and cleaning. Said problems can be prevented by the use of hollow-fibre membranes. Optimization of the diameter of the fibre and of the choice of membrane material provides hollow-fibre membranes which are highly suitable for use in the method according to the present invention.
Preferably, the hollow-fibre pervaporation membrane is internally coated with poly(dimethylsiloxane) (PDMS) and/or ethylene-propylene-diene monomer (EPDM). PDMS is commercially available, e.g. RTV 615A (trademark from GE Silicones). To enhance the mechanical strength as well as the durability it is advantageous for the polymeric PDMS chains to be cross-linked prior to use. This can be effected by means of the cross-linking agent RTV 615B from GE Silicones. EPDM, in many varieties, is marketed by DSM-Elastomers, inter alia. A good EPDM coating is formed by the type Keltan(copyright) 578 from DSM-Elastomers, which likewise should be cross-linked prior to use, for example with the aid of a peroxide such as dicumyl peroxide. In the case of internally coated hollow-fibre pervaporation membranes, the extract is passed through the hollow fibre (the feed side). On the other side of the membrane (the permeate side), water and especially the desired aromas are abstracted from the feed by a partial pressure difference across the membrane. After pervaporation an aroma-depleted retentate remains which, if desired, can be used for the recovery of the valuable substances which may still be present therein, such as catechols, fats and aromatic substances, in particular bitter flavourings which, if desired, can subsequently be added to the aroma concentrate according to the invention. It is also possible for the hollow-fibre membrane to be provided externally with a thin separating top layer of PDMS or EPDM. In this case, the feed is passed along the outside of the fibres and the permeate is formed in the interior of the fibres. This configuration is less suitable, however, than using an internally coated pervaporation membrane and passing the feed through the fibres, since the separation efficiencies are considerably poorer, owing to moderate hydrodynamic flow conditions on the feed side, and cleaning of the outside of the fibres is problematic.
The pressure on the permeate side is preferably kept below 30 mbar. Depending on the separation requirements, a permeate pressure of between 1 and 30 mbar is required. At lower pressures, more permeate will be collected, but at relatively high pressures, between 10 and 30 mbar, better separation efficiencies are possible.
As described above, it was found that for the method according to the invention a temperature of 30xc2x0 C. or more gives statisfactory separation characteristics.
Preferably, the pervaporation process is carried out at a feed temperature of more than 60xc2x0 C. So far, a temperature of between 30-80xc2x0 C. has proved highly advantageous. This means that the feed (the food extract) during the pervaporation process has a temperature in the said range. Pervaporation preferably takes place at as high a temperature as possible, for example at the extraction temperature. A feed temperature above 80xc2x0 C. is not possible at the moment, since present-day membrane materials available may become damaged above the said temperature. In principle, the pervaporation process is therefore not limited to feed temperatures up to 80xc2x0 C.
It should therefore be understood that the pervaporation temperature may depend on the desired aromas to be obtained. If the aromatic substances in question are unstable above 60xc2x0 C., for example, care should be taken to ensure that the pervaporation takes place below this temperature. The extraction should then obviously likewise take place at a temperature below 60xc2x0 C.
The permeate is preferably obtained by cooling in a condenser system and by collecting it in liquid condensed form. This condensate mainly comprises water (or some other extractant used) and the desired aromas. The temperature at the condensation is preferably around xe2x88x9220xc2x0 C. or below. At this temperature, most of the aromas condense from the permeate.
To obtain a concentrated aroma concentrate it is preferable for the permeate to be cooled in a first condenser at a temperature of between 0xc2x0 C. and 15xc2x0 C., preferably between 3xc2x0 C. and 8xc2x0 C., the copermeated water, in particular, being condensed from the permeate and the uncondensed material, which comprises the major fraction of the aromas, then being condensed at xe2x88x9220xc2x0 C. or below, preferably below xe2x88x9280xc2x0 C. In this two-stage condensation, the water is condensed at the higher temperature and is thus removed from the aroma. In the second condensation step, the concentrate and any remaining water is condensed and thus collected. Whilst condensation is to be preferred for collecting the concentrate, other ways of binding the concentrate from the permeate are also known in the art, for example binding to a carrier such as activated carbon.
In particular, the invention relates to a method as described hereinabove for isolating cocoa aroma concentrate, wherein the food base material comprises a cocoa-comprising material, preferably cocoa powder.
The invention further relates to food aroma concentrate obtainable via the method according to the invention. In particular, such an aroma concentrate comprises less than 0.5% (w/w) of fat and is preferably substantially fat-free. As the pervaporation membrane is impermeable to fats, a food aroma is obtained which is substantially fat-free. (That means less than 0.05% (w/w) of fat.)
The invention further relates to a food aroma concentrate which comprises less than 0.005% (w/w) and preferably less than 0.001% (w/w) caffeine. The last-mentioned value corresponds to 0.01 g/l of the recovered condensate. It was found that the method according to the invention affords a food aroma concentrate comprising permeate which comprises less than 0.01 g/l of caffeine. The invention also relates to a food aroma concentrate which is obtainable via the method according to the invention and which, in analogy to the above-described, comprises less than 0.005% (w/w) theobromine and/or catechols, preferably less than 0.001% (w/w).
The invention further relates to a food aroma concentrate obtained in accordance with the method according to the invention, wherein the aroma has also been admixed with at least a portion of the retentate of the pervaporation. As already explained hereinabove, the retentate may still comprise important substances. In the case of recovering cocoa aroma concentrate according to the invention, the bitter flavourings, for example, substantially remain behind in the retentate. Whilst this is advantageous in obtaining a less bitter cocoa aroma, a small amount of the said bitter flavourings is desirable in certain cases to obtain a pleasant cocoa flavour. To obtain such an aroma, the said bitter flavourings can be added to the food aroma concentrate, for example in the form of the retentate of the pervaporation step. In a preferred embodiment, the invention relates to a food aroma which is obtainable in accordance with the method according to the present invention and which is cocoa aroma prepared from cocoa powder or some other cocoa-comprising food.
Cocoa aroma concentrates obtained according to the prior art have often been obtained via an alcoholic extraction and therefore have a considerably higher fat content. The cocoa aroma concentrates obtainable via the method according to the present invention, wherein substantially no fat is taken up into the extractant, are highly suitable, because of their low fat content, for foodstuffs whose fat content, for example, is critical. Moreover, the organoleptic taste sensation of the cocoa aroma concentrate according to the invention is considerably better than that of the present-day cocoa aroma concentrates. Moreover, the cocoa aroma concentrates according to the invention are soluble in water, colourless and, as explained hereinabove, substantially fat-, caffeine- and theobromine-free. Furthermore, the aroma concentrate according to the invention substantially comprises no microbiological activity, which represents a very high added value.
The invention further relates to a cocoa aroma concentrate which, on the basis of the total mass of the condensed material of a two-stage condensation, comprises less than 0.01% protein, less than 0.01% fibres and less than 0.05% sugars. In this context reference should be made to Table 2. Such a concentrate has not previously been known in the art and can be obtained by the method according to the invention. It was found that such a concentrate has optimal gustatory qualities and can advantageously be used in the bakery, dairy and soft-drinks industries. Present-day cocoa aroma concentrates are of inferior quality and more difficult to handle.
The invention further relates to a food and a food concentrate which comprises an aroma concentrate, in particular a cocoa aroma, according to the invention.
Table 1 below gives a schematic overview of the various characteristics of aroma concentrates obtained by liquid extraction, steam distillation, supercritical extraction and by pervaporation. Pervaporation is to be understood as a combination of liquid extraction, followed by pervaporation.
The above demonstrates that pervaporation differs from all the other extracts in that no purines and catechols are detected in the extract. In extracts obtained by means of methods other than pervaporation, said presence is detectable, in contrast, or at any rate it cannot be ruled out that they are present.
Liquid extraction was carried out in accordance with the following Example 1, steam distillation was carried out in accordance with (U.S. Pat. No. 3,579,349), the supercritical extraction was carried out in accordance with the following Example 6.
The pervaporation was carried out in accordance with Example 7.
The following Table 2 shows a characterization of the feed and the aroma concentrate in the case of a one-step concentration and a two-step condensation in accordance with the invention as carried out in accordance with Example 7.